Pembentukan Citrarinaldi.munir/Citra/...menyatakan pemantulan total. •Jika permukaan mempunyai...

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Pembentukan Citra IF4073 Interpretasi dan Pengolahan Citra Oleh: Rinaldi Munir Program Studi Teknik Informatika Sekolah Teknik Elektro dan Informatika Institut Teknologi Bandung 2019

Transcript of Pembentukan Citrarinaldi.munir/Citra/...menyatakan pemantulan total. •Jika permukaan mempunyai...

  • Pembentukan CitraIF4073 Interpretasi dan Pengolahan Citra

    Oleh: Rinaldi Munir

    Program Studi Teknik InformatikaSekolah Teknik Elektro dan Informatika

    Institut Teknologi Bandung2019

  • Model Citra

    • Secara matematis fungsi intensitas cahaya pada bidang dwimatra disimbolkan dengan f(x, y), yang dalam hal ini:

    (x, y) : koordinat pada bidang dwimatra

    f(x, y) : intensitas cahaya (brightness)

    pada titik (x, y)

    x

    y

    f(x,y)

  • • Karena cahaya merupakan bentuk energi, maka intensitas cahaya bernilai antara0 sampai tidak berhingga,

    0 f(x, y) <

    • Nilai f(x, y) sebenarnya adalah hasil kali:

    i(x, y) =jumlah cahaya yang berasal dari sumbernya (illumination),nilainya antara 0 sampai tidak berhingga, dan

    r(x, y) = derajat kemampuan obyek memantulkan cahaya

    (reflection), nilainya antara 0 dan 1.

    • Jadi, f(x, y) = i(x, y) r(x, y),

    yang dalam hal ini,

    0 i(x, y) < 0 r(x, y) 1

  • permukaan

    sumber

    cahaya

    i(x,y)

    normala

    f(x,y)

    Sinyal f(x,y) ini yang ditangkap oleh mata atau kamera

  • The scene is illuminated by a single source.The scene reflects radiation towards the camera.The camera senses it via chemicals on film.

  • • Nilai i(x, y) ditentukan oleh sumber cahaya, sedangkan r(x, y) ditentukan oleh karakteristik objek di dalam gambar.

    • Nilai r(x,y) = 0 mengindikasikan penyerapan total, sedangkan r(x,y) = 1 menyatakan pemantulan total.

    • Jika permukaan mempunyai derajat pemantulan nol, maka fungsiintensitas cahaya, f(x, y), juga nol.

    • Sebaliknya, jika permukaan mempunyai derajat pemantulan 1, makafungsi intensitas cahaya sama dengan iluminasi yang diterima oleh permukaan tersebut.

  • Contoh-contoh nilai i(x, y):

    • pada hari cerah, matahari menghasilkan iluminasi i(x, y) 9000 foot candles,

    • pada hari mendung (berawan), matahari menghasilkan iluminasi i(x, y) 1000 foot candles,

    • pada malam bulan purnama, sinar bulan menghasilkan iluminasi i(x, y) 0.01 foot candle.

    Contoh nilai r(x, y)

    • benda hitam mempunyai r(x, y) = 0.01,

    • dinding putih mempunyai r(x, y) = 0.8,

    • benda logam dari stainlessteel mempunyai r(x, y) = 0.65,

    • salju mempunyai r(x, y) = 0.93.

  • Pinhole camera

    • This is the simplest device to form an image of a 3D scene on a 2D surface.

    • Straight rays of light pass through a “pinhole” and form an inverted image of the object on the image plane.

    Sumber: Image Formation Fundamentals, CS491E/791

  • Camera optics

    • In practice, the aperture must be larger to admit more light.

    • Lenses are placed to in the aperture to focus the bundle of rays from each scene point onto the corresponding point in the image plane

    Sumber: Image Formation Fundamentals, CS491E/791

  • Image formation (cont’d)

    • Optical parameters of the lens• lens type

    • focal length

    • field of view

    • Photometric parameters• type, intensity, and direction of illumination

    • reflectance properties of the viewed surfaces

    • Geometric parameters• type of projections

    • position and orientation of camera in space

    • perspective distortions introduced by the imaging process

    Sumber: Image Formation Fundamentals, CS491E/791

  • What is light?

    • The visible portion of the electromagnetic (EM) spectrum.

    • It occurs between wavelengths of approximately 400 and 700 nanometers.

    Sumber: Image Formation Fundamentals, CS491E/791

  • Short wavelengths

    • Different wavelengths of radiation have different properties.

    • The x-ray region of the spectrum, it carries sufficient energy to penetrate a significant volume or material.

    Sumber: Image Formation Fundamentals, CS491E/791

  • Long wavelengths

    • Copious quantities of infrared (IR) radiation are emitted from warm objects (e.g., locate people in total darkness).

    Sumber: Image Formation Fundamentals, CS491E/791

  • Long wavelengths (cont’d)

    • “Synthetic aperture radar” (SAR) imaging techniques use an artificially generated source of microwaves to probe a scene.

    • SAR is unaffected by weather conditions and clouds (e.g., has provided us images of the surface of Venus).

    Sumber: Image Formation Fundamentals, CS491E/791

  • Range images

    • An array of distances to the objects in the scene.

    • They can be produced by sonar or by using laser rangefinders.

    Sumber: Image Formation Fundamentals, CS491E/791

  • Sonic images

    • Produced by the reflection of sound waves off an object.

    • High sound frequencies are used to improve resolution.

    Sumber: Image Formation Fundamentals, CS491E/791

  • CCD (Charged-Coupled Device) cameras

    • Tiny solid state cells convert light energy into electrical charge.

    • The image plane acts as a digital memory that can be read row by row by a computer.

    Sumber: Image Formation Fundamentals, CS491E/791

  • Frame grabber

    • Usually, a CCD camera plugs into a computer board (frame grabber).

    • The frame grabber digitizes the signal and stores it in its memory (frame buffer).

    Sumber: Image Formation Fundamentals, CS491E/791